This invention relates to a ground fault detector for use with a leak current interrupter, and more particularly to improvements in a waveform shaper circuit included in a ground fault detector.
Conventional ground fault detectors have been previously formed of mechanical elements but several years ago it is forwarded to compose them of electronic elements because of their poor characteristics. This measure has permitted the zero-phase-sequence component current transformer for converting ground fault currents to corresponding voltages to be made small-sized resulting in the advantage that ground fault detectors can be constructed inexpensively. Electronic ground fault detectors have generally comprised the amplifier for amplifying a signal corresponding to a detected circuit resulting from a ground fault occurring on an associated electric system, the time delay circuit for delaying an output signal from the amplifier, the waveform shaper circuit for shaping a waveform of an output current from the time delay circuit, and the thyristor responsive to an output current from the waveform shaper circuit to be conducting, the conducting thyristor being operative to drive a mating circuit interrupter to interrupt the electric system. Since the waveform shaper circuit supplies the output current to the thyristor through a resistor thereby to put the thyristor in its conducting state, the output current from the wave shaper circuit is decreased when the thyristor is conducting to operate the circuit interrupter. This has resulted in the disadvantage that the waveform shaper circuit can not continue to supply a gate current to the thyristor. This disadvantage has attended with other disadvantages that the ground fault detectors can not be operated in stabilized manner and also the waveform shaper circuit has a high consumed power resulting from the gate current as determined by the resistor connected thereto.
Accordingly, it is an object of the present invention to provide a new and improved ground fault detector including a switching element operative in stabilized manner with a low comsumed power.
It is another object of the present invention to provide a new and improved ground fault detector excellent in temperature characteristics.